1. Field of the Invention
The present invention relates to a process for preparing a graft copolymer. More particularly, it relates to production of a graft copolymer having a feature in the initiator used whereby the grafting process is improved.
From another aspect, the present invention relates to a process for graft copolymerization onto a halogen-containing resin.
2. Related Art
Copolymers in the form of a "comb" having "branch" polymers grafted onto a "backbone" or "trunk" polymer by chemical bonds are generally called graft copolymers including those having "branch" polymers with low molecular weights.
While graft copolymers in the form of a comb are prepared by the method for chemically bonding a polymer for the branch (typically a so-called macromonomer) which, has been preliminarily prepared to a polymer for the backbone, the graft copolymerization method regarded as the conventional method comprises the formation of a polymer for the branch and of the branches by the "in situ" method, that is, specifically the polymerization of a monomer for forming the polymer for the branch in the presence of a polymer for the backbone.
The conventional method includes the methods in which the polymer for the backbone is in a melted form, in a solution or in a dispersion (i.e. emulsion or suspension), which are not always free from problems.
More particularly, while the method for copolymerizing a monomer for, branch polymers in the presence of a polymer for the backbone in a melted state requires no additional process for grafting because the process can be carried out in a melt kneader provided in an extruder, the reaction is carried out at a temperature equal to or higher than the melting point of a given polymer for the backbone, such as about 200.degree. C. and such method cannot be utilized in fact in such cases as the monomer to be used tends to be deteriorated thermally or is volatile or corrosive to metal. While such problems will not be found when the polymer for the backbone is in the form of solution, a problem still remains for recovering a solvent used, which is an organic solvent when the polymer for the backbone is other than water soluble polymers. Furthermore, it is also required to recover a graft copolymer, which is obtained in the form of solution in the solvent used, from the solution for example by the distillation of the solvent used or by the addition of a solvent less compatible with the copolymer unless the graft copolymer produced is used as such in the form of solution.
On the other hand, the method for using a polymer for the backbone in the form of dispersion has no such problems as described above and has already been widely adopted industrially to such cases as production of a so-called ABS resin wherein acrylonitrile and styrene are polymerized in a polybutadiene latex.
In either of the aforementioned methods, a monomer which is used as a monomer for the branch polymer to be polymerized in the presence of a polymer for the backbone, however, tends to polymerize itself instead of "graft" polymerization onto the polymer for the backbone and thus had a problem that the "graft ratio" which is a ratio of the monomer graft copolymerized to the total amount of the monomer used may not be increased sufficiently without special consideration for the initiation of the polymerization of the monomer for the branch polymer. Although no serious problem will occur due to the presence of a non-"graft" polymer which actually forms no "branches" when some advantages are obtained by the presence of the non-graft or non-branch polymer as in the case, for instance, of the ABS resin wherein the copolymer of styrene and acrylonitrile which has not grafted onto the polybutadiene may constitute the resinous portion of the ABS resin, it is desirable to have a graft ratio as high as possible from the standpoint of the intrinsic object of graft copolymers.